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MV Model 3P OB Loudspeaker Project

BHamm

BHamm

The pendulum swings.
This thread is to publicly thank MJKing for sharing a recent speaker build he designed on his website dated 2-21-15. I wanted to build an earlier design he posted on his website but the Fostex drivers used in that build are no longer available. These Open Baffle speakers are short and angled back 15 degrees so they point at the listener. They use the Eminance Alpha 15A woofer and Fostex FF85WK full range.

I have them positioned 3 feet off the back wall and in a 7 foot equilateral triangle. It should be stated I have never before heard OB speakers. The crossover is a simple second order that uses a 120uf resistor on the woofer. I decided to try a MRC of the same value. I've had them playing all day and I must say I am impressed. My main speakers are KEF R700s. My first impression was they do a lot of what the KEFs were doing. Sound stage is there as well as imaging and detail. I need to spend more time listening but they definitely have my attention. Thanks MJKing and all the AK posters in the Open Baffle threads:thmbsp:
 

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Very nice! Congratulations on the nice lookin' build! :banana:

Make sure you spend time playing around with placement, tilt angle and spacing them up. It'll help you learn what they can do.

Welcome into the simplicity and yet musically rich OB experience. Hope you get some quality time listening this weekend. :music:

EV3
 
I have them playing with a pair of Anarchy Tapped Horn subs. I haven't even tuned the subs for the OBs yet, but everything sounds fantastic. I'm still trying to wrap my head around this sound I'm hearing.
 
BHamm,

Nicely done, the speaker look great. I thought this OB design performed way beyond the modest cost.

I wonder if you could do me a favor and run a test on your speakers. Swap the plus and minus leads to the Fostex driver and give the speaker a listen both ways. One way will sound a little darker due to a mild depression around 500 Hz in the SPL response, the other connection produces a flat SPL response. It should be a clearly audible result. Let me know which connection (drivers in phase or out of phase) you prefer.

I lent my pair out and forgot to confirm that I had wired the crossover correctly, I like the flat response better and I think my diagrams are all in order but have not been able to double check. I believe the flat response has the Fostex wired with reverse phase compared to the woofer. No rush, I am just curious.

Thanks in advance,

Martin
 
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When I reverse the Fostex leads the bass is more pronounced. I'm going to listen with the new setting for a while.
 
Good advice, and these weigh almost nothing compared to my usual speakers.:thmbsp:

evsentry3 said:
Very nice! Congratulations on the nice lookin' beuild! :banana:

Make sure you spend time playing around with placement, tilt angle and spacing them up. It'll help you learn what they can do.

Welcome into the simplicity and yet musically rich OB experience. Hope you get some quality time listening this weekend. :music:

EV3
Click to expand...
 
Martin,

I tried measuring the response this morning using a crude method. I had a decibel meter at my listening spot and fed test tones through the speakers wired both ways. Unfortunately there was no noticible difference in SPL, but I did not have a 500hrz tone. Only 1k hrz and then 200hrz. I thought the depression would show itself anyways, but it did not.

While listening to music last night, I thought I could hear a slightly fuller bass with the Fostex wired in reverse. I was able to check several times while listening. If you confirm later on, can you advise me if I have it right.

Thanks again,

Bryan

MJKing said:
BHamm,

Nicely done, the speaker look great. I thought this OB design performed way beyond the modest cost.

I wonder if you could do me a favor and run a test on your speakers. Swap the plus and minus leads to the Fostex driver and give the speaker a listen both ways. One way will sound a little darker due to a mild depression around 500 Hz in the SPL response, the other connection produces a flat SPL response. It should be a clearly audible result. Let me know which connection (drivers in phase or out of phase) you prefer.

I lent my pair out and forgot to confirm that I had wired the crossover correctly, I like the flat response better and I think my diagrams are all in order but have not been able to double check. I believe the flat response has the Fostex wired with reverse phase compared to the woofer. No rush, I am just curious.

Thanks in advance,

Martin
Click to expand...
 
Bryan,

Here is what I found with my pair.

When the Fostex and Eminence were wired in phase there was a broad dip between 250 Hz and 600 Hz. This made the speaker sound heavier in the bass because the mid bass was recessed, the lowest bass does not change. The speaker had a darker sound, the deeper bass was more dominant.

When the Fostex and Eminence were wired out of phase the dip was filled in and the SPL was smoother in this frequency range. The speaker sounded a little brighter and the mid bass was more present.

I don't think either connection is bad it is just a matter of taste. I listened to both connections for a few days each and decided I like the out of phase connections better, this produced a smoother SPL response which to me was more enjoyable. But I am more of a midrange listener and not such a bass head.

Martin
 
Martin,

Thanks for getting back. I do prefer the out-of-phase wiring. I was just reading about second order crossovers and how they are susceptible to phase shift. Not sure if that is what was going on, but thanks for explaining things.

With my crude measurements, in my room, the OBs play down in the 50 hrz range. I adjusted my subs accordingly and have a full, engaging sound from these little butt-kickers.

Cheers

MJKing said:
Bryan,

Here is what I found with my pair.

When the Fostex and Eminence were wired in phase there was a broad dip between 250 Hz and 600 Hz. This made the speaker sound heavier in the bass because the mid bass was recessed, the lowest bass does not change. The speaker had a darker sound, the deeper bass was more dominant.

When the Fostex and Eminence were wired out of phase the dip was filled in and the SPL was smoother in this frequency range. The speaker sounded a little brighter and the mid bass was more present.

I don't think either connection is bad it is just a matter of taste. I listened to both connections for a few days each and decided I like the out of phase connections better, this produced a smoother SPL response which to me was more enjoyable. But I am more of a midrange listener and not such a bass head.

Martin
Click to expand...
 
Congratulations! They sure look nice.

I wouldn't have thought such a minimal baffle would get you bass down to 50. Hats off to MJK too!
 
PastTechFan said:
I wouldn't have thought such a minimal baffle would get you bass down to 50.
Click to expand...

It is all about engineering the design with simulations; I can try any OB baffle arrangement, drivers, and crossover combination in minutes and know how it will perform. No trial and error, no risks, the results are very predictable.
 
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